1. Field of the Invention
The invention relates to a capstan of the type utilized in high performance tape drives employed in computer applications. The invention provides improved tape handling characteristics by dampening capstan resonance.
2. Description of the Prior Art
In constructing high performance tape drives for computer applications it is important that the drive be able to rapidly reverse the direction of tape movement and, upon reversal, bring the tape from zero speed up to the performance speed (which may be as high as 200 inches per second) in the shortest possible time. Most employ a single capstan affixed directly to the shaft of a motor. The performance of the tape drive is affected by the resonance characteristics of the motor or, more precisely, the motor armature, the motor shaft and the capstan.
In order to permit most rapid acceleration or deceleration of a magnetic tape, it obviously is highly desirable that the capstan have minimum inertia. To accomplish this, capstans have been designed with are extremely light and yet rigid. Maximum efforts have been employed to devise capstans of minimum rotational inertia with required strength. Each capstan has an inherent resonant frequency. In plotting the resonance characteristics of a tape drive system, it has been found that when reducing the load inertia of a capstan for driving a short section of magnetic tape, problems are encountered in the structural design. As an example, in the case of a capstan which is structurally sound enough to drive the tape but flexes enough to allow capstan resonance at a point below the armature resonance and within the servo and data electronic band width, the performance of the tape drive is impaired. In attempting to solve this problem using the straight-forward approach of increasing the material in the capstan to reduce flexing and thereby attempting to move the resonance point outside the servo and data electronics band width, the capstan mass goes up. The increase in the mass offsets the increased stiffness of the capstan, and therefore, this attempt to solve the problem is more or less self-defeating. In addition, it is important that the tape drive be designed so that the capstan and armature/shaft resonance are not superimposed. To prevent this occurrence, then the resonance point of the capstan is below the armature/shaft resonance, much mass must be added to the capstan to raise it to a point so that its resonance is above the armature/shaft resonance to prevent superimposition. Thus, it would be highly advantageous to maintain the capstan at a minimal mass condition if some means could be found to dampen the portional resonance below the critical point of the tape drive servo loop.
It is therefore an object of this invention to provide a means of improving the performance of a tape drive by reducing the effect of the capstan resonance without materially increasing the mass of the capstan and while maintaining the resonance at a point below that of the armature/shaft resonance.
Another and more general object of this invention is to provide a capstan having improved dampening characteristics, or, stated in another way, to provide a low inertial capstan dampening means.
These general objects as well as other and more specific objects of the invention will be fulfilled in the following description and claims, taken in conjunction with the attached drawings.